Python3 字典的增删改查

增加:

　　1. 直接通过索引添加dic["key"]=value

dic = {"A":"a","B":"b","C":"c"}
dic["D"]="d"
print(dic) #{'A': 'a', 'B': 'b', 'C': 'c', 'D': 'd'}

　　2. 通过dic.setdefault("key","value")

dic = {}
dic.setdefault("A","a")
print(dic) #{'A': 'a'}

删除:

　　1.　ret=dic.pop("key")　

dic = {"A":"a","B":"b","C":"c"}
dic.pop("A")
print(dic)  #{'B': 'b', 'C': 'c'}

　　2. del dic["key"]

dic = {"A":"a","B":"b","C":"c"}
del dic["C"]
print(dic) #{'A': 'a', 'B': 'b'}

　　3. dic.clear() 清空字典

dic = {"A":"a","B":"b","C":"c"}
dic.clear()
print(dic) #{}

改:

1.通过索引直接改 dic["key"]=value

dic = {"A":"a","B":"b","C":"c"}
dic["C"]="d"
print(dic) #{'A': 'a', 'B': 'b', 'C': 'd'}

2. 通过 dic1.update(dic)更改

dic = {"A":"a","B":"b","C":"c"}
dic1 = {"A":"a","B":"b","C":"d","D":"c"}
dic1.update(dic) #把dic的内容更新到dic1里面,如果key重名,就修改,如果不重名就添加
print(dic1) #{'A': 'a', 'B': 'b', 'C': 'c', 'D': 'c'}

查:

1. dic["key"]  直接通过索引查, 没有key的时候会报错

dic = {"A":"a","B":"b","C":"c"}
print(dic["C"])  #c

2. dic.get("key") 没有key的时候会返回None

dic = {"A":"a","B":"b","C":"c"}
print(dic.get("B"))  #b
print(dic.get("D"))  #None
print(dic.get("D","d"))  #d  字典中没有对应的key时,返回指定的值"d"